Those icicles can be so enticing. But licker, beware. Whether it’s an icicle, an ice cube or (less frequently, we hope) a metal pole, sometimes the tongue hits something very cold, and it won’t let go. Why is that?
The easy answer is that the saliva on our tongues freezes solid, creating a steadfast connection. But there’s more to it than that, scientists say. For instance, why do our tongues rarely stick to an icy-cold plastic or wooden object?
You can blame something called thermal conductivity, which is a measure of how fast heat flows through a material. It can vary wildly depending on the type of material. The higher the conductivity, the faster heat moves. Your fingers may have learned a painful lesson in this when you burned them trying to stir a boiling pot with a metal spoon, which is an excellent conductor. But with a wooden spoon, you feel barely any heat: The thermal conductivity of stainless steel is 150 times that of wood.
Objects in contact with each other attempt to reach a thermal equilibrium, so something at a higher temperature (the boiling soup) will transfer heat to the cooler object (the spoon). Same thing with your tongue and anything icy: It will surely rob your warm tongue of heat. However, the key question is: How rapidly will it do so? A metal pole exposed to freezing temperatures will quickly steal heat away from your tongue, faster than body heat can come to the tongue’s rescue. The result is that your saliva freezes solid inside all the nooks and crannies of your tongue. You are stuck.
Frozen plastics and wood are not as good at sucking heat away quickly, so your body heat wins. Ice isn’t as efficient as metal is at sucking heat away, but it’s more conductive than plastic and wood.
Ideally, warm water can be used to melt the frozen bond and free whatever appendage happens to be stuck. Breathing warm air onto it may also help. But perhaps the best advice is to avoid getting cemented in the first place.